Meltwater is water that is released from melting snow or ice. This includes meltwater from glacial ice and ice shelves over oceans. Meltwater is often produced during volcanic eruptions, and can cause dangerous lahars (landslides of wet volcanic debris). When meltwater pools on the surface rather than draining or flowing away, it forms pools known as melt ponds. Meltwater will often refreeze as the temperature drops. Meltwater can also collect or melt under the ice's surface. Sub-glacial...